2.2. Data Collection and Study Variables
The children’s DMFT scores were based on clinical examinations performed by two well-trained and calibrated dental practitioners (kappa = 0.87) [15]. The DMFT score has been well established as the key measure of caries experience in dental epidemiology, reflecting the degree of caries experience, and is calculated by adding results for Decayed, Missing due to caries, and Filled Teeth in the permanent dentition. Visual examination by means of an artificial white light source and plane mouth mirror was combined with probing diagnosis in caries examination, with codes and criteria as established by the WHO [16]. The information on grade of intellectual disability and the presence or absence of cerebral palsy was supplied by the special education school. Every child with a disability had been examined and assessed by the designated and qualified hospital. The results of the assessment were registered in the school’s medical records.
A self-administered parental questionnaire (11 items) was used to collect data on socio-demographic characteristics and oral health behavior variables. Socio-demographic variables included the gender of the children, parental education level, registered residence, and school district. The parental education level was categorized into “lower education” (1–12 years), “‘medium education” (13–15 years), and “higher education” (16 or more years) [17]. Grade of intellectual disability and the presence/absence of cerebral palsy were based on the criteria established by Standardization Administration of the People’s Republic of China and WHO respectively [14,18]. Oral health behavior variables, as used in previous
research, included gargling habits after meals, dental visits in the preceding 12 months, frequency oftoothbrushing, eating snacks, and eating sweet foods before sleeping [17,19–21]. In total, 477 questionnaires were delivered, and 450 valid questionnaires were returned, for a return rate of 94.3%.